External fixators have been in use for over a century. The first recorded use was by Wilhelm Wutzer (1789-1863) who used pins and an interconnecting rod in a clamping system to repair badly broken bones. Parkhill (1897) and Lambotte (1900) used unilateral devices with four pins and a bar/clamp system. By the 1960's, Vidal and Hoffman popularized using external fixators for open fractures and infected pseudarthroses. The problems expressed with fixation in the late 20th century, however, were mostly due to lack of understanding about its basic principles of application and healing. Therefore, external fixator (or “EF”) use was relegated to the most severe of injuries wherein infections, pin problems, non-unions, and mal-unions were all too common.
Since the 1950's, Ilizarov took developed principles and expounded on the ring and wire style of then, external fixation devices with excellent success. It was not until the late 1980's and early 1990's, when there was better communication with the Western world (after the fall of the former Soviet Union), that the methods of Ilizarov and thus, external fixation, were more easily demonstrated to the West. External fixation has now become so refined that it is now a potent tool in the management of orthopedic fractures, with or without complicated conditions. Currently, in the United States, external fixators have two widespread uses: in a damage control orthopedics (DCO) frame which is meant to be temporary, and in a treatment frame intended for a longer term, definitive treatment.
When external fixation is used for deformity or limb salvage, the device may require certain abilities for successful treatment. It should be able to lengthen and shorten as well as correct angular or rotational deformities. The original wire fixator design of Ilizarov utilized rings and tensioned fine wires that were connected together into an assembly with threaded rods. Use of hinges, and other accessories allowed the device to correct numerous conditions. These included all of the pre-requisites of lengthening-shortening, angular and rotational deformities. However, due to its completely manual nature, it required a significant amount of expertise and management. Subsequently, many surgeons in the United States did not employ the device routinely.
Some time later, the Taylor Spatial frame was developed using the science of the Stewart Platform, a device used to develop flight simulators. It allowed for a programmable multi-axis motion. The Taylor Spatial Frame utilized the hexapod mechanism of the Stewart Platform. It is placed on a limb segment with a ring above and below the deformity. The relative position of the rings to each other is readily known by the position of each of the six struts of the hexapod construct. The position of the construct to one limb segment is also known by use of radiographic measurements. Thus, by virtue of the known relationship of one limb segment to one ring, and the rings to themselves, the opposing limb segment's position is known since it is technically part of the same rigid body of the second ring.
Using a web based software program, the parameters can be used to create a corrective prescription that results in a relative motion between each ring, and therefore, each limb segment. A radiographic measurement of the resulting correction is performed and if needed, another iteration of the program for correction is performed, to result in a residual correction. Each corrective iteration is described by a prescription that outlines the adjustments in each hexapod strut. These maneuvers are performed manually by the surgeon or patient. Currently, the Taylor Spatial Frame is the only device available that provides a semi-manual three dimensional correction.
Other available fixators that can provide three-dimensional adjustments are mono-planar and utilize a series of hinges. These are not progressively adjustable like the struts of the Taylor Frame, and there is no web based software program that can be used. Some efforts at providing a uni-axial correction, e.g., axial motion such as a lengthener, have been developed. Still, these devices require experience for correct placement and are manually driven.
The device in the present patent utilizes the characteristics of both the mono-planar fixators as well as kinematic programming to effect a three dimensional correction of two limb segments. Instead of a ring-hexapod methodology, however, this fixator utilizes a mono-planar or series of mono-planar segments that have one or more electromechanical elements that can effect motion automatically. The elements are positioned in a prescribed arrangement around the limb, and its relationship to the limb segment is established. Each electromechanical element has a known position relative to others and to the limb. Using known 3-D kinematic calculations, the corrective formula can be determined, and signals to each motorized element determine the rate and amount of correction.
The said elements can have the ability to communicate using standard wireless technology, and can retain a history of position, force, and rate. Such electronic and recording capability can also be used to establish the compliance of the patient and working reliability of the device. The fixator described in this report can be attached to any fixator element in each limb segment. The ability to attach to a ring, a clamp, or other pin-bar construct allows its use with a variety of other products, and it is subsequently functioning as a connecting rod.
Several studies have tackled the different healing patterns of fractures in various external fixators. These studies have all attempted to measure fracture callous stiffness and strain during healing for outlining “how” healing occurs. The basic principle is that of progressive load transfer. If a bone fracture is going to heal, ensuring a proper load transfer to develop callous is necessary. The first stage of external fixation attempts to achieve a rigid and still construct for allowing induction of the healing process as well as letting the adjacent soft tissues time to “recover”. Once that biologic potential is realized, the EF frame progressively “de-stiffens” to transfer more and more load to the newly developing callous. If the construct is made too flexible, too early, the resultant strain may exceed the limits of that callous. And if there is not insufficient EF load transfer, some bone resorption and disuse osteopenia may result, both of which are undesirable. EF de-stiffening can be performed by removing bars, adjusting the location of bars, or removing certain pin/wire components.
With ring EF designs, the load transfer is usually a repetitive stimulus that occurs with increasing functional activity. As healing progresses, wires and half pins get removed and/or support struts loosened. Finally, some of the intervening struts can be removed altogether, leaving ring/wire/pin constructs with the patient having a trial weight bearing. If there is clinical pain, the struts get reapplied with the presumption that healing is not yet complete.